Radio communication system



Dec, 7, 1937. J. B. BISHOP Er AL RADIO COMMUNIQATIONiSYSTEM 6Sheets-Sheet? Filed Sept. 26, 1935 /NVENTORS J. B; B/SHop 'W M. KNOTT B.yg/J

ATTORNEY www www

Dec. 7, 1937. J. B. BISHOP E1- Al.

RADIO COMMUNICATION SYSTEM Filed Sept. 26, 1935 6 Shets-Sheet 3 MNM.

m. .Usl

7, 1937. y J B; Hops ET AL 2,101,668 I RADIO COMMUNICATlEON SYSTEM Filedsept. 26,` 1935 e-shets-sheet 4 J. B. BISHOP /NvENTo/Psw M KNO".

A TTORNEV uw.v 7, 1937. J: B. BISHOP T AL. 2,101,668

v 4RADIO coMMNIcATIoN SYSTEM 6 Sheets-,Sheet 5 Filed sept. 2e, 1935935.6 Etam E 1Mb www ATTORNEY 75 l937- J. B. BlsHoP T AL imnoCOMMUNICATION SysTEM Filed sept. 26, 1 935 6 Sheets-*Sheet 6 P 0 H S l BB. `J uuu dzfdm w w No 31 ma wbb wmmwb QU 5S w ma 1% Qu SMS/ m M Klv-OTTl V ATTORNEY.

Patented Dec. 7, 194374.

RADIO COMMUNICATION sYs'rEM John B. Bishop, Bloomfield, e and william M.

Knott, Fairlawn, N. J., assignors to Bell Telephone Laboratories,Incorporated, N. Y., a corporation of New York New York,

Application september ze, 1935, serial No. 42,112

^ 12 claims.

This invention relates to radio communication systems and particularlyto two-way radio communication systems and control circuits therefor.

An object of the invention is to provide a system for two-Way 4radiocommunication which will meet the requirements of reliability, economyof operation, simplicity of control and the like, essential to a two-waycommunication system for commercial operation.

w One obstacle to the use of radio for communication is the lack ofdependability. This fault is partially an inherent characteristic ofradio Y transmission and is due to atmospheric disturb.

v ances, lskip distance effects, and the like. Since as far as ourpresent knowledge is concernedthese difficulties must be accepted, it isnecessary to adopt some method of overcoming their effects. It is wellknown that atmospheric disturbances while present to some degree atnearly all frequencies, do not affectv all frequencies equally.

Further, skip distance effectsv can be made to serve a useful purposefor carrying a signal over a maximum distance with a minimum of power.To take advantage of these conditions it is necand receiver and if theservice is to approach the reliability of other types of communicationservice such a shift of frequencies should be ac-A complished with theleast possible delay.

A particular object of the invention is to prov ide a radio transmitterwhich may be operated on lany of a number of frequencies and which canbe readily shifted from one frequency to another in a minimum time andwith a minimum of control operation.

Another object of the invention is to provide a radio transmitter whichcan be mounted at an isolated point andv operated unattended except forcontrols from a remote point for turning von and off `the power andautomatically and rapidly controlling the frequency.

`Anotheryobject of the invention is to provide means for reducing theconsumption of power in remotely controlled radio transmitters.

Another object of the invention is to provide interlocking control meansbetween a radio transmitter and a radio receiver'so that two-waycommunication may be carried on without interference in the receiverfromthe local transmitter. These and 9121.1?? objects of the invention haveessary to shift the frequency of the transmitterA (Cl. P18-44) beenaccomplished by the arrangement to be described in connection with theattached drawings, which, when arranged as shown in Fig. 7, showschematically one embodiment of the invention in a combined radiotransmitter and receiver for 5 two-way 'communication by telephone ortelegraph.

Radio transmitter The mechanical structure of the radio transmitter isof the type disclosed and claimed in the patent of H. D. Wilson, No,2,077,160, issued April 13; 1937, and comprises five removable chassislocated in a vertical arrangement from bottom to top as follows:Oscillator chassis Bill, first 15 buffer amplifier chassis 5H), secondbuffer ampliiler chassis E20, modulating amplifier chassis 530. andoutput circuit chassis 560. Each of these ve removable chassis isequipped to accommodate as many as ten individual plug-in units whichmay be selected and adjusted to operate at any carrier frequency withinthe desired range. The oscillator chassis accommodates up to ten quartzcrystal'plates Gli and a like number of oscillator coils SI2. (In eachcase only the first and last of the series of ten are shown). The rstand second buffer amplifier and modulating amplifier chassis eachaccommodate up to ten tuning units,.0il, Sil and 53|, respectively. Theoutput circuit ,chassis is arranged to provide for ten tuning coils 5M.

In addition to these removable chassis the transmitter houses themechanism which is actuated by the teelphone dial 620 to select one often elevator rods 605. Each rod actuates a series of bell cranks such as608 to closel switches in the various chassis completing all the neces-0 sary circuits for setting up a particular frequency. The first andsecond buffer amplifier stages are sometimes used to amplify thefrequency generated by the crystal oscillator and .at other times one orboth are used as frequency doublers, depending upon the carrierfrequency desired. In this Way, for example, crystal frequencies rangingfrom 2000 to 4525 kilocycles serve to yield a range in output frequencybetween 2 and 18.1

megacycles.

In addition to the radio transmitter circuit proper there is provided,as shown in the circuits 9,f Figs. 3 and 4. a power supply, voicefrequency 50 amplifier and control circuit. The power supply circuitincludes necessary rectiiiers for obtaining from an alternating currentsource all the power voltages including plate and grid bias and filamentheating current together with a rectifier for obtaining direct currentfor the operation of the microphone and all control relays.

Radio frequency circuits Before going into the details of the operationof the control circuit of the radio transmitter, the

operation of the radio frequency circuit of the transmitter will bebrieiiy considered. As indicated above, there is employed in thisequipment a crystal oscillator, two successive stages of intermediatepower amplification or frequency doubling, a modulating amplifier and apower amplifier. When M. C. W. telegraph or telephone transmission isemployed the modulation electromotive force is applied to the plate andscreen of the modulating amplifier tube 532 which immediately precedesthe final or power amplifier stage employing a three-element amplifiertube 542. For convenience in describing the circuit let it be assumedthat the switching equipment has been operated to select the first or Achannel so that all of the switches 60|-A,

602-A, 50i-A, 502-A, 50S- A, 504.-A, S05-A, 50B-A, 50`|A and 508-A havebeen closed. Switch 60|-A completes the grid circuit of the oscillatortube 6|3 while switch 602-A completes the plate circuit for the sametube. The plate circuit of this oscillator is coupled to the gridcircuit of the first intermediate power amplifier tube 5|2 through thecoupling condenser 6|4. The tuning unit 5| l--A connected in the platecircuit of the tube 5|2 serves as the complete potential.

tuned circuit in the plate circuit of the tube 5|2. If this stage is tofunction as an amplifier the circuit 5| I-A is tuned to the crystalfrequency. If the stage is to function as affrequency doubler thecircuit will, of course, be tuned to double the crystal frequency.

The output of this stageis coupled to the grid of the tube 522 in thesecond intermediaite power stage through the condenser 5|3. Connectedin'the plate circuit of the tube 522 by means of a switch 502-A is thetuned circuit 52|-A which functions for this stage in a similar mannerto the circuit 5| I-A of the previous stage.

The output of this stage is coupled to the grid of themodulating-amplifier tube 532 through the coupling condenser 523.Connected inthe plate circuit of this tube 532 by means of the switches503-A and S04-A is a tuned circuit 53|A which, of course, is similar inits frequency characteristics to the circuit 52|-A of the previousstage. The switching circuit of the modulating amplifier stage 530differs from that of the intermediate power amplifier stages in thatneither end of the tuning unit 53 I -A is at ground This is occasionedby the fact that the power amplifier tub'e 542 is of the three-elementvariety and requires a neutralizing voltage which is supplied to thelower end of the tuning unit 53|-A through the switch 503-A when closed,a neutralizing circuit of the capacity bridge type being used. When bothswitches 503-A and 504-A are closed excitation is applied to the grid ofthe power amplifier tube from the junction of condensers 533 and 534.Switch 505-A shortcircuits a portion of the resistor 55| and leaves thecorrect amount of resistance in the plate supply in the modulatingamplifier tube 532, The

power amplifier stage has its circuit completed by a tuning coil 54|-Awhich is adjusted to properly tune this circuit when the switches 50G-Aand 50i-A are closed.

Dialing channels B. C, D, etc. likewise serve to select the properelevator rods which, in a simi'- lar 'manner to that described above,lcomplete the entire tuning to the frequencies associated with theserespective channels.

The transmitter is designed to work directly into a 50G-ohm load and isequipped with ten independent output terminals which connect to the tenoutput circuits through the switches 50B- A to 50B-J. One additionaloutput terminal 533 is common to all channels. This arrangement allowsfor ten independent 50G-ohm transmission lines connected to terminals 50I-A to BBI-J and leading to ten antennae, or one 50G-ohm transmissionline common to all channels connected to terminal 533 and terminated inan antenna tuning unit.

In the crystal oscillator chassis 3|0 is located a self-startingsynchronous motor 330 and in parallel with this motor on the left panelare two indicator lamps 03| and 332 which are lighted while the armatureof the motor 330 is rotating. 12-volt alternating current is supplied tothe oscillator chassis from the connection 634 to the groundedconnection 333. This voltage serves to energize the heaters SI5-A SI5-Jfor the quartz crystal plate and also to periodically operate the motor630 and supply power through the rectifier BIS to operate the crystalheater relays 6|1A SI1-J. As soon as power is supplied to the rectifiercircuit by the closing of switch 402, 12-volts alternating current issupplied to the line 394 and the circuit of the motor 630 is initiallycompleted through the upper contact of the crystal heater relay 3H andthe commutator 635 associated with motor 530 and the commutator armrotates to the lower of the two contacts associated with that particularcrystal. It thus breaks its own circuit which is not again com'- pleteduntil the heater relay SI1 operates. When the relay 3|1 operates themotor 530 is again started and the commutator arm moved to the firstcontact associated with the next heater relay wherel it remains untilthat crystal has gone through its heater cycle. In this way theindicator lights 59| and 832 function only when each and every crystalheater is properly operating. Should any one crystal'fail to operate themotor 530 would stop and the indicator lights would remain permanentlyoff. When the crystals are all properly functioning in their heatercycle the indicator lights periodically blink. Should any one crystalheater fail the indicator mark on the motor driven commutator 335 willshow which crystal is at fault. In the event that a crystal is not usedin one or more of the stages such stage or stages may have their leadsgoing to the motor armature bridged so that the indicator clears thatpoint immediately.

Operation of cfmtrolcircuits Power is supplied from the three-phasealternating current mains 40|. As soon as the main power supply switch402 is closed the alternating current bus-bars of the transmitter areenergized through the voltage regulating transformer 403 and thetransformers 404 and 405 are energized, transformer 404 supplying12-volt alternating current for heating the quartz plates in thetransmitter over the connection 534. Transformer 405 furnishes f8-voltdirect current for aromas of the rst close energizes relay 62|, the48-volt circuit for the operation of this relay being completed toground through the contact 633 of the switch 660 and the contacts of thedial 620. i A circuit is simultaneously closed from the48-volt directcurrent source through the operating magnet 622 of the selector, therebystretching its return spring.

The instant of first open releases the selector armature by opening thecircuit of the` operating magnet 622 so that the armature is then pulledback by the spring causing the brushes of the four contacter groups 64|,642, 643 and 644 to rotate to position I. Relay 62| remains operateddueto its slow release characteristic and nothing else happens.

The next instant is that of second close. When the selector operatingmagnet 622 and the relay 62| each again simultaneously receive a pulseof energy which pulls the selector operating magnet 622 up (relay 62| isalready operated and thus remains unaltered'in this position).

T he next or second open period follows immediately whence the selectorarm moves to position 2 and nothing further happens until relay 62|releases at the end of its slow release period (about one-quartersecond). When relay 62| releases 48' volts is supplied throughthe lowerarmature of. relay 62|: (l) through the third selector bank 643 to relay624.and through lead 425 to relay 4|3 which is simultaneously operatedby current supplied through the rectiler-r'esistance network 401, and(2) through contact 63| of .switch 630 and fourth selector bank 644 toenergize the latching relay 603--B (not shown but identical to relay603-A) As soon as relay 624 has operated, its holding circuitthrough thecontacts of the time delay relay 625 keeps it energized, and two'resultsfollow:

(1) Its lower armature completes a circuitfto the elevator rod contactor604 which is actuated and moves the rod S05-B, due to the operation ofthe latching relay BB3-B, to its up position and also starts theVentilating fan 606 which is connected in parallel with the contactor604.

(2) Through its upper armature 48-volt direct current circuit to therelay 4|3 is additionally closed thus forming a holding circuit for therelay 4|3. This circuit may be traced from lead 425, upper armaturerelay 624, armature relay 625, lower armature relay 62| to the 48-voltcircuit 682.

When the elevator rod contacter 604 is actuated it mechanicallyoperatesa switch 630. The operation of the switch 630 results in thefollowing simultaneous events:

(1) The holding circuit to the latching relay BB3-A is broken at `thecontact 63|, the armature of the latching relay 603--B beingmechanically held in place due to the force exerted on the push rod60E-B.

(2) Arm 632 makes contact with its upper contacts completing a circuitthrough the selector operating winding 622 through the selector bank 64|so that the `selector mechanism automatically notches itself back'to itsnormal position.

v (3) Contact arm'633 breaks its connection with its lower contact andmakes connection with the upper contact preventing the relay 62| fromreafter the elevator rod contactor 604 has completed the setting up ofone of the 4radio channels.

The 48-volt direct current supplied over the lead 426 by the operationof the circuits described above energizes the relay 4|3 through thenetwork 401 as previously described. 'I'he operation of this relay 4|3causes the operation of the filament heating circuit contactar 4||through the circuit completed from the alternating current bus-bars 490through the inner contacts of the relay 4|0 and normally closed contactsof relays4l9 and 420.V 'I'he operation of the contactor 4|| causes thesimultaneous energization, from the alternating current bus-bars of theA transformer 426 (all radio and grid bias rectifier tube filaments).transformer 428 all high voltage rectier tube filaments) and transformer328 (the audio-amplifier tube filaments) The operation of the contacter4|| simultaneously with the energization of the transformer 426energizes parallel connected winding of the time delay relay 4|5 whichis timed to operate 35 seconds later. When relay 4|5. operates the biasplate supply transformer 430 for the grid bias rectifier is energized.This circuit may be traced from the alternating current bus-bar 49|,lead 49|, transmitter gate switches 5|9, 529, 639, 549 and 562,rectifier gate switch 449. contact and armature of relay 4|5 to primaryof transformer 430 and upper armature of filament contactor 4|| tobus-bar 492. This causes 20()` volt directl current to be produced bythe.grld bias rectifier tubes 43| and this appears across the outputresistance network 432. This rectified voltage is supplied to themarginal relay 4103 and energizes it.

When relay 406 operates, its lower armature completes the circuit to oneside of the high voltage contactor 4|2, provided the switch 439 isclosed or provided relay l||`| is energized by the operation of themicrophone press to talk button 459 as described hereinafter. Thiscircuit may be traced from the connection of the busbar 49| at thearmature of relay M5, through lower armature of relay 408. switch 439 orlower armature of relay (lll to the lower terminal of the winding ofhigh voltage contacter M2. The

upper armature of the relay 408 completes the ground side oi the L8-voltdirect current circuit through the coil of the relay 4|4 and operatesit. As a result of the operation of relay M4 the following sequence ofevents takes. place:

(1) Relay 4|3 is short-crcuited through the upper inner armature ofrelay 4|4 and drops out.-

(2) A holding circuit for relay 4 I4 is completed through the upperouter armature.

(3) A holding circuit of the filament contacter 4|| is completed throughthe lower outer armatures of the relay 4|4 and lower contact of thecontacter 4| I.

(4) The lower inner armature of the relay 4|4 'completes a circuit tothe other side of the high voltage contactor 44|2. 'I'his circuit may betraced from the bus-bar 492, through armatures ofy relays 4|3 and 420,lower inner armature of relay 4|4, lead 432, contact 634 of switch 630and lead 033 tothe upper terminal of the winding of the high voltagecontactor 4|2.

When the high voltage contactor 4|2 is ener gized it operates toenergize the high voltage transformer 33| which, in turn, completes thenecessary high voltage to the plates of the high voltage rectifier tubes432 and consequently to furnish direct current to the plate of thevacuum tube forming the circuit of the transformer proper. It alsoprovides power to the filament transformer 333 of the voice operatedcontrol circuit 300 described later.

The operation just described sets up the circuit for the operation ofthe transmitter. The other relay circuits will be described later underthe headings Automatic control features for push button, and Voiceoperated control, respectively.

Direct current power supply The three-phase high voltage rectifiersdelivering 2500 volts and 800 volts are employed to furnish directcurrent power to the plate circuits of the power amplifier andaudio-amplifier tubes and to the low power radio frequency tubesrespectively. Each high voltage rectifier uses three of the rectifiertubes 332, all of the tubes receiving their alternating current platevoltages from the single three-phase transformer 33|. The 2500-voltsupply is delivered through the filter circuit comprising 'theinductance coil 334 and the condenser 335 and the 800-volt supplythrough the filter comprising the inductance coil 336 'and condensers331. A potentiometer filter circuit consisting of the resistances 33Band condenser 339 serves to furnish aproximately 200- volt directcurrent to the screen grid circuits of the tubes to the first and secondbuffer amplifier stages and to operate the hang-over relays of the voicefrequency control circuit 300, to be described later.

As described earlier, an independent full wave rectifier employingtwotubes 42| and delivering a total of 20D-volt direct current is used tofurnish grid bias to the power amplifier and modulating amplifier tubesthrough an appropriate filter circuit consisting of the inductance coil420 and condenser 433. A potential divider 432 supplies 12o-volt biasthrough`the filter coil 434 and condenser 435 to .the tubes of thebuffer amplifier stages.

Speech input and monitoring circuit Speech or tone input to theaudio-amplifier is brought in over the lines 305-306, for example, fromthe operators control circuit as will be described in detailhereinafter, or may be obtained from a local telephone set plugged intothe jack 409 in which case it will be supplied through the transformer301 to the connections 305-306.

In any event such tone input is supplied to the primary of thetransformer 308. When a local telephone set plugged into the Jack 403 isused, direct current for the telephone transmitter is supplied from thef8-volt rectifier 406 through the filter 4 0 and the microphonetransformer 301.

A transformer 4|6 has its primary circuit paralleled by a resistor 4|8connected in series in the plate return of the power amplifier tube 542.The secondary winding of' this transformer is terminated by therectifier type voltmeter 42| for indicating the modulation level. Theterminals to the secondary of the transformer 4|| are also provided forconnecting to the 0perator's set as described hereinafter. For adjustingthe modulation level a resistance pad attenuator (not shown) may beinserted in the' leads to thevprimary of the transformer 308.

The audio-frequency amplifier comprises two tubes 309 and 3| 0 connectedin tandem. The circuit is so arranged that it receives its high voltagepower from the 2500-volt rectifier supplied through theresistor-condenser filter 34|. The grids of both tubes are biased by thedrop in the plate current fiowing through resistances connected in thereturns to the cathodes. The tube 309 receives its entire plate and gridsupply from the voltage drop across resistor 3|| which also furnishesgrid bias for the tube 3|0. The grid bias for tube 303 is supplied fromthe drop in the cathode return resistance .343.

A relay 3|2 is provided so that when operated it short-circuitsv thegrid input to tube 3|0 through its upper armature and thus prevents thecarrier from being modulated. This relay is for the purpose of C. W.telegraph control since its use allows for controlling the carrier bythe method of' keying the tone input without at the same time producinga modulated C. W. signal. The relay 3|2 may be controlled either locallywhen the transmitter is on any channel or automatically when aparticular channel is dialed as will be described in detail hereinafter.

The output of the tube 3|0 is supplied through the transformer 342 tothe plate and screen grid of the modulating amplifier tube 532 tomodulate the radio frequency carrier in that tube.

Voice control circuits A voice control circuit 300 comprising vacuumtubes 323 and 324 and associated relays and equipment is provided forcontrolling the operation of the transmitter, particularly for acombined transmitter and receiver circuit, by the voice or tone input.Speech input is supplied to the grid of the flrst tube 323 through thetransformer 325 which has its primary winding connected in the platecircuit of the first audioamplifler tube 303 in parallel with theprimary winding of the interstage transformer 344. The tube 323 isself-biased by the cathode return resistor 32B, the plate voltage beingsupplied from the 20G-volt output of the rectifier tubes 43|. The platesupply for the second tube 324 is furnished from the plate supply of theassociated radio receiver through the connection 321, as will bedescribed in detail in connection with the operation of the circuit. v

Control unit 300 functions in the following manner: When the speech ortonesupplied to the input terminals 305, 306 reaches a predeterminedlevel. say minus 60 decibels, it-then produces a sufficient increase inthe plate current of the second stage tube 324 to operate the platerelay 3|3, plate current being supplied from the B battery supply of theradio receiver. When the relay 3|3 operates two events take place:

4l-The grounded armature pulls away from the back contact which isconnected through the armature and contact of relay 3|4 and retard coil3|6, relay 601, to the plate supply for the oscillator tube 6|3.

2-When the grounded armature of the relay 3|3 touches its front contact.the circuit for the windings of relays 3|4 and 3|5 is closed to groundso that these relays are operated. The current/ flowing from thepositive 25o-volt terminal of the voltage divider 333 through connection3| 1,- resistances 3|9, the windings of relays 3|5 and 3|4 CII - voltcircuit.

The relays M4 and lli are designed to provid 'l "hang-over" in theoperation o! the voice control circuit. 'Ihe relay I4 is held up forapproximately 150 milliseconds atterthe armature cirelay SI2 hasreturned to its normal position by the discharge of the condenser 32| sothat it serves wheny operated to insure that the oscillator controlcircuit does not' become grounded until some 150 milliseconds after thelast passage of speech. Relay Il! is given an additional time `delay dueto the discharge of condenser 24| to remain operated from 8 to 10milliseconds after relay 214 has returned to normal and is usedftoprevent the associated radio receiver from returning to an operatecondition before the carrier output of the transmitter has beencompletely suppressed. t

Relay N8 which maybe operated either locally or automaticallyl onpredetermined dialed chan` nels is for the purpose oi modulated C. W.carrier control. Its upper amature functions to disable the hang-overrelay N4 by short-circuiting the winding thereof and thus allowsV thetransmitter to produce a modulated C. W. signal by the method of keyingthe tone input.

Key clicks are eliminated by the use of the retard coil 218 placed inseries with the oscillator control. circuit thus preventing the carrierfrom dropping or bumping to zerowhen relay 3I4 d returns to its normalposition.

. erations.

Automatic control features for ltmslt-lnttton control of carrier d Twotime delay relays 422 and 625 are providedV by means of which full'automatic operation of the transmitter 'may be secured. These relaysare controlled by two switches 422 and 628.

-Switch 423 is known as the automatic illament release switch and 6254as the automatic high voltage release switcha Switch 423 is in serieswith the winding of the relay 422 so that in the open position of theswitch relay 422 cannot be energized. Switch 626 parallels the contactsof relay B sol that even though this relay were operated no effect wouldresult as long as switch 826 remained closed. For full automaticoperation of the transformer therefore switch 626 is normally open andswitch 422 is normally closed. Both time delay relays 422 and 625 may betimed to operate in a period such as 1 to 15 minutes.

When the transmitting equipment is arranged for push-button operation,it performs two op- Flrst, the outer armature. with the switch 439 open,is in series with the winding of the high voltage contactor 4I2 so thatthis contactor will V'only be closed when the relay 4|1 is operated bydepressing the key 450. In other words for push-button lcontrol the key45| controls the entire plate supply to the transmitter and hence thecarrier output. A be observed that relay 411 in its normal unoperatedcondition, through its inner amature, allows the 48-volt direct currentsupply to be applied to the coil of the time delay relay 425` throughconnection 424. inner armature of relay 4I1, and connection 426. Thiswould result in the operation of. the relay 42| in from 1 to 15 minutesdepending upon its adjustment after a amines. Y

,of relay 42B opens the holding circuit to the rel Second, it will layU24 which results in two events:

l l-Elevator-contact 404 dropsdown, releasing the channel which had beendialed.

2-The return 48-volt circuit through connection 42| is broken .and asthe'result relay 4I4 is deenergized andtherefore dropped out. Theholding circuit to the filament contactor 4II is 'still energized,however, throughthe back 4contact of relay 4I! so that the illaments ofall the tubes inv both units still remain heated.

Summing up then, the action of relay 425 can serve only to drop down thechannel which has been dialed in the transmitter and disrupt the 48`voltreturn circuit to the rectier controls.

, Itis important to note that in the normal opera- 'I'hertime delayrelay 422 is energized throughs the normally closed back contact to the'normally closed contact -of the lower armature of the high voltagecontactor 4I2. At the end of this l to.

ing oi' the overload relay 419. thus opening the circuit to the coil ofthe illamentcontactor 4H which immediately removes all lament voltage'.-

As soon as the lament contactor 4| I has dropped out,` the alternatingcurrent circuit actuating the 15 minute period relay 422 operates and inclosv ing puts'a pulse of current from the 48-volt source through theconnection 431 to the wind,

relay `422 is deenergized. Thus the momentary circuit made to theoverload relay 4|9 is broken and relay 4I9 returns to its normal(closed) position, and providing relay 62B has previously operated, thevtransmitting equipmentl is back to .the condition it originally was whenonly the mainpower supply switch 402 was closed..l

It is VVimportant to note here that it is immateriai whether the relay422 operates prior or subsequent to the relay 825. Each performs itsfunction independently of thel other.` This is not true as will beevidenced in the latel` description, in the event that the use of thevoice frequency control unit 30d is substituted for the push-buttoncontrol. (In this latter event relay l 422 must of necessity operatesubsequent to relay Returning tothe case in point, namely thelpush-button operation, it is seen thatthe total elapsed time over whichuse may be made of these automatic shut-down features is conned to atime not exceeding fteen minutes (with relays oi.' the characterdescribed) Should it be desired to have the high voltage remov'edfromvthe tubes of the transmitting equipment but have the illaments remainheated, it is necessary only to throw switch 423 to the open position inwhich case it would be necessary either to manually close the switch422'and wait the delay period of therelay 422 or to momentarily open themain Apower .supply switch 402. t

'Automatic control features for voice operated control of carrier Whenvoice control of the carrier is employed.

through the use of the control unit 300 switch 4321s closed and switch438 is opened. Closing 4switch 439 by-passes the particular function ofthe relay 411 which for push-button control use exercises the finalcontrol of the high voltage applied to the radio tubes of thetransmitting apparatus, current will flow from the 800-volt supply atthe terminal of filter coil 338 through the oscillator plate resistor6H, relay Bill, back to ground through the choke SIG vand the armaturesof relays 3M and SII. This current will operate relay $01 at once andcause the time delay relay 625 to be energized from the f8-volt supplylead 682. After the predetermined time of operation of the time delayrelay 825, it will operate as earlier described, to drop down thechannel and since the release of the channel opens the interlocks atcontact 634 to the high voltage contactor M2, this contactor will bereleased. As soon as the high voltage contactor M2 drops out, thecircuit will be completed through its lower armature to energize therelay 422 which will operate after its predetermined time has elapsedand as described in the section .immediately preceding, will operate onthe filament contactor lll to remove all power from the transmittingequipment -except the crystal heater circuit and the 48-volt rectifiersupply.

Incoming speech, subsequent to dialing and having high voltage appliedtothe transmitting equipment, removes the ground return at the armatureof the relay Sil and since no current flows in this circuit, relay 601is released which in turn deenergizes the time delay relay B26 returningits timing mechanism to the initial position. Thus, the operation of thetime delay relay 625 commences at the cessation of incoming speech ortone or from the last starting operation in the absence of an incomingsignal.

It is important to note in this connection that the start of the timedelay relay |22 commences from the operation of the time delay relay825, rather than from the start of that relay as was the case withpush-button control as described in the previous section.

Auxiliary control feature 'I'he relay SI2 associated with theaudio-ampliiier may be actuated by connecting the bus 635 to one or moreof the ten points on the bank G42 of the selector. This relay isprovided only for the purpose .of converting the radio transmitter intoa C. W. telegraph transmitter and is used only in conjunction with thecontrol unit 300 as will be described hereinafter in the sectionentitled, C. W. and M. C. W. telegraph operation.

Similarly, the bus 636 when connected to appropriate terminals on thebank 842 of the selector actuates the relay Sil and is used to convertthe radio transmitter into a M. C. W. telegraph transmitter. Thisconnection also is used only in conjunction with the use of the controlunit 300 and its operation will be described in detail in the sectionentitled, C. W. and M. C. W. telegraph operation.

Protective circuit Protective gate switches are applied on the apparatusto insure that the operating personnel is adequately protected againstcoming in accidental contact with high voltage. For this purpose thereis provided a gate switch Il! on the door to the transmitting equipmentand switches 549, B39, 529 and 8| which are opened when any of therespective chassis I, l, III or M are removed from their cradles.Bimilarly, gate switches4 I are associated with the rectifier assembly.All of these gate switches are connected in series in circuit from thearmature l and contact of relay 4N through which the grid bias rectiertransformer 430 is energized.

Two self-restoring overload relays III and I!! are provided to protectthe vacuum tube against Switching mechanism 'I'he switching mechanism asshown and described in detail in the copending application of H. D.Wilson, hereinbefore referred to, consists, in brief, of ten rods 80G-Ato 80B-J running the vertical length of the transmitter. Cranks, such as60S-A, for example, one for each chassis switch, are located onhorizontal cross shafts mounted normal to the elevator rod. A mechanismto operate the elevator rods is located at their lower ends.

'Ihis mechanism includes the shaft |50 mounted in self-aligningbearings. One end of this shaft passes through an adjusting block to thearmature of the large alternating current operated solenoid 604. Mountedon the shaft GIU are a series of clutch collars BSI- A to lil-J andassociated lifting arms B52- A to 6524. 'I'he clutch collars are pinnedto the shaft "I by taper pins while the lifting arms 852 are free toboth slide and rotate on the shaft. Associated with the clutches aresmall. latching relays BDI- A and 60S-J for actuating the clutches toengage the lifting arms.

The operation of the switching mechanism is briefly as follows: When thearm of the selector switch comes to rest momentarily on one of theoff-normal contacts the voltage supplied to one of the'small latchingrelays 003 causes the armature of the relay to close and draw with itits lifting arm, which slides along the shaft to engage the clutchcollar. At the same instant that voltage is supplied to the latchingrelay I, voltage is also supplied to relay 624 which picks up and inturn closes the 250-volt circuit to the large solenoid elevatorcontactor 804. The elevator contactor i now closes and in doing sorotates the shaft 050 with the clutch collar and the one lifting armwhich has been previously engaged. 'I'he other nine lifting arms merelyallow the shaft to rotate within them and remain in their non-operatedpositions.

The outer end of the lifting rod Il! which has been engaged to rotatewith the shaft comes to bear on the lower end of its elevator rod llland in turn pushes it upward. The elevator rod 605 transmits its upwardmotion by means of the bell cranks, such as |08, to an axial thrust inline with the chassisswitches such as ill.

At the same time that this is happening the switch arms of the switch 0have been changed from their normal to their closed position by means ofthe lever arm mechanism lll. As here- -inbefore described in moredetail, this switch `telegraph features by dial control.

performs several functions, one oi which is to remove the voltage lfrom-the latching relay 003 by breaking the circuit at contact 03|. 'I'heserelays are designed for intermittent purpose only and their solefunction is to engage the lifting-arm with its clutch, the two beingfirmly held together bythe frictional load when the elevator rod 805 israised.

If another channel is dialed the circuit to the large solenoid 604 isbroken on the first puise of the dial and the armature of the solenoidfalls back to the open position aided by a return spring (not shown) andthe load of the operated elevator rod 605. to disengage from its clutchas soon as the elevator rod has reached its bottom stop at which pointthe return spring 654 on the armature of Automatic C. W. or M. C. W.telegraph operation When control unit 300 is employed the'transmittingequipment may be made to function as a` C. W. or a M. C. W.telegrapntransmitter by operating either relay SI2 or relay 3|0,respectively, and keying the tone input through thel key 218 at theoperators control position as Will be described in detail hereinafter.The relays mayjbe operated by the control switch 20d at the operatorsposition, or may be operated automaticallyv when predetermined numbersare dialed.` In this latter case switch dit must be closed and the busesB and 63E are connected to the proper terminals of the selectorcontacter tt2. As' illustrated contact i is connected to bus 635 andcontact 3 to bus 636. Thus, when i is dialed, the set will operate forC. W. telcgraph and when 31s dialed, for M. C. W. telegraph. Switch t'iis closed only for operation of the When these features are controlledby the operators switch 233, 4the switch M5 is kept open as illustrated.

When i is dialed the set will be conditioned for C. W. telegraphoperation by the automatic operation of relay 3|2 through the closing ofits operating circuit by the contacts on the selector bank iiilZ. Whenthe selector bank M2 returns to its normal position, relay dit ismaintained `operated through a holding circuit from lead Md In a similarmanner when t is dialed,'connec tion will be made through the selectorbank ttt which will result in automatic operation of the relay 3|8,which also has' a holding circuit y Athrough its lower armature similarto relay 3|2.

Thus keyed rtone input in this case will merely result in starting andstopping of the modulated carrier in accordance with the keyed impulses.

A more detailedv description of the keying operation will be found underthe title Radio telegraph communication in the following section ontwo-` consists in addition to the lradio transmitter andits controlcircuit just described, a radio re- This allows the lifting arm 062Aceiver |00 and an operators control unit 20| which are interconnectedwith the transmitter 'I'he radio receiver |00 which is shown in blockdiagram, only the parts essential to the interlocking control featurebeing sown in detail, is of the typical superheterodyne type employingan initial Vselector circuit |02 connected between the antenna |0| andthe radio frequency'ampliiler |00. The output of the amplier iti issupplied through another selective circuit (not shown) to the highfrequency detector or modulator |03, the latter being supplied withbeating waves from an oscillator |04 for combining with the receivedwaves to-produce intermediate frequency waves which are selectivelyamplided in an intermediate frequency amplier |00. The output of thisamplifier is supplied to the input of the detector H01 which operatesnot only to detect the intermediate frequency waves to produceaudio-frequency waves which are amplified in the audio-frequencyampliiler |08, but also to vrectify the intermediate frequency carrierto supply the automatic volume control circuit iii of the conventionaltype. For the reception of continuous wave telegraph signals there maybe provided a heterodyne oscillator and .detector (not shown). `For amore detailed description of a radio receiver of this type reference ismade to the copending application oi H. T. Budenbom, Serial No. 676,135,filed June 16, 1933.

While grid bias supply and plate lsupply are indicated as furnished bybatteries i i2 and it@ for simplication in illustration it is understoodthat such power supply would normally lbe derived from rectifiedvalternating current inl a wellknown manner.

Associated with the radio receiver is a control circuit |20 which may beconditioned by the operation of the key |2| for operation for eitherCodan (carrier operated device anti-noise) con- .trol or Vodas (voiceoperated device anti-singing) control. In the case of both types ofoperation the controlcircuit |20 operates to block the output of theradio receiver to the 'connected telephone station at all times except.when there is an incoming :signal to the radio receiver as will bedescribed in detail hereinafter. This control circuit also operates toprevent the use of the radio transmitter when a signal is being receivedand also, in eiect, to disconnect the radio transmitter monitoringcircuit from an extension telephone circuit when transmission is beingcarried on. In so doing it prevents feedback from the radio transmittermonitoring circuit to the speech input circuit by way of a twoconductorextension telephone line but allows the operators telephone receiver tobe connected at thesame time to both the. radio transmitter monitoringcircuit and the radio receiver output circuit in order to lpermitmonitoring in both directions of a radio telephone circuit.

The control of the radio receiver |00 to disable it for the reception ofradio signals is accomplished by means of relays |09, I|0 and Whenoperated, relay |09 grounds the antenna K |0| through its front contactand opens the ground circuit for the grid of the tube of the CII theconnection through its back contact to the grids of the tubes of theradio frequency ampli- `Iier and modulator |03 through the automaticvolume control circuit H3 and instead closes a connection for the gridsof those tubes to the battery I2 to block the tubes. The operation oirelay opens the connection to the coils of the Silent coil group ||4 sothat they act in series opposition preventing transmission therethrough;This transmission control is of the type disclosed and claimed in SilentPatent 1,749,851, March 1l, 1930. Operated -relay opens the contacts andso arranges the connections between the interconnected windings of thetransformers oi the group ||4 that these windings are mutually opposed.Thus, no transfer `of energy between the circuits connected through theother windings of the transformers of the group ||4 may be eected.Consequently. passage of audio-frequency current from detector |01 tothe audio-frequency amplifier |90 is prevented.

A second Silent coil group 2|| is employed in the operators controlequipment to permit the.

operator to monitor simultaneously both sides of a radio telephoneconversation of a two-wire telephone extension circuit. This coil group2|| also serves as an added precaution against objectionable clicks andother circuit noise incidental to the operation of control relays whichmight otherwise reach the subscribers telephone receiver. The control ofthis coil group is effected by the relay |22 of control circuit |20. Theoperation of the relays which control the two Silent coil groups and 2||is so timed that the audio-frequency circuits are always disabled whenother control relays are being operated.

Radio receiver control circuit 120 The control circuit provides voice orcarrier operated control of the radio receiver output circuit when it is`rinterlecked with the voice operated control of the radio transmittercontrol circuit 300 in such av manner that operation of the radioreceiver control relay |22 will prevent operation of the radiotransmitter, as will be described in detail hereinafter.

Vacuum tube |23 is of the dual function type and comprises a full waverectier employing the anodes |24 and a three-element section comprising.the grid |25 and anode |26, both sections having a common cathode |21.Space current for the amplifier section is supplied from a directcurrent supply such as battery4 |28 through a Wheatstone bridge circuithaving as three arms thereof the resistors |29, and |3| and as thefourth arm `the cathode-anode path |21-|2|. The operating winding |34 ofthe relay |22 is connected'across one diagonal of the bridge.

Two potentiometers |32 and |33 are provided for controlling the balanceof the bridge, one potentiometer being for Codan operation and the otherfor Vodas operation. The conditioning of the circuit for either type ofoperation iscontrolied by the operation of key 2|. When this key is intheleft-hand position as shown the circuit is conditioned for Vodasoperation. In this condition, in the absence of arecelved signal in theradio receiver |00. the potentiometer |33 is adjusted to vary the biason the grid |25 of the tube |23 until the bridge is balanced and nocurrent ilows through the winding |34 of relay |22. Under suchconditions the relay |22 will beheld in its normal position by thecurrent in the polarizing winding |39 which current is the normal spacecurrent of the tube 324 of the control unit 300 supplied from thebattery |40; i. e., the plate current in the absence of a speech or toneinput to the control unit 300. When a speech modulated carrier isreceived in the receiver |00 the speech output current is suppliedthrough the lead |36 and transformer |31 to the full wave rectifiercomprising the anode |24, cathode |21 and tube |23. The voltage producedacross the resistance |38 by the rectied voice currents is impressed onthe grid |25 of tube |23. The effect of this voltage will be toimbalance the bridge and cause current to flow through the winding |34of the relay 22 to oppose the action of the polarizing winding |39. Whenthe current through the winding |34 becomes sufficient to produce a iiuxgreater than that produced in the relay by the polarizing winding |22,through which the normal (non-operating) space current of the ampliertube 324 of the control circuit 300 is iiowing, the relay armature willtransfer from the left-hand contact to the right-hand contact.

In the operation of the control circuit |20 for the Vodas type ofoperation sufficient hang-over for the control relay |22 to preventdisabling of the Silent coil group between words of speech is providedby means of the condenser |42 which is charged by incoming speech to thepotential developed across the rectiiler load resistance |38. Thecondensers discharge slowly through the resistor |38 upon completion ofa passage of speech to maintain the radio receiver control relay |22 inoperated condition for say approximately 150 milliseconds after the lastpassage of speech.

This operation of the relay |22 performs two functions which are: (l)When the armature leaves its normal (left-hand) contact it breaks thecircuit from the high voltage supply |40 of the radio receiver |00through the receiver disabling relays ||0 and |09 and the control relay3|3 of the controlr unit 300 to the tube 324. In this manner the radiotransmitter is completely disabled until the bridge circuit regains itsnormal condition when the incoming signals cease; (2) when the armatureof the relay |22 reaches its operated contact it connects together thefour inner ends of the windings of the transformers of the Silent coilgroup 2| I. With the transformer windings so connected theaudiofrequency output from the radio receiver may pass through the coilgroup 2|| to the operators control circuit 200.

When the relay |22 is in its normal condition l vare impressed on thetransmitter circuit and also during the hang-over time for thetransmitter control circuit 300, in the latter case through theoperation of the relay` 3|5, current through the winding |39 will besuillcient to hold the relay in its normal positionso that the currentproduced in the winding |34 by the action of the voice output of thereceiver will be insufllcient to operate the relay. After voice currentsin the transmitteiceases, the space current of the tube 324 falls, andconsequently the polarizing current through the winding |39, to acomparatively small value so that the relay may be operated by theaction of the currents in the winding |34.

The hang-over operation produced by relay 3|5 is suchthat the circuit321 will be closed to ground through the armature of relay 3|5 andresistance 389 for 8 to l0 milliseconds after relays 7'5 lay |22polarized to disable the receiver during this period. i

For Codan operation of the radio receiver control circuit |20 thenegative bias supplied to the grid |25 to cause the operation of therelay |22 -with an incoming carrier, is obtained from the loadcircuit'oil the detector |01 through the lead I4 'Ihis negative voltageis supplied to the grid |25 through the middle contact of the switch |2|when in its right-hand position. In this position of 'the key |2| thegrid |25 is initially biased by the voltage across the potentiometer|32. By the adjustment of this potentiometer the normalgrid bias can beadjusted to apoint where no current ows through the winding |34 of thecontrol relay when no carrier is received by the radio receiver. In asense this gives the relay |22 the power to discriminate between noiseand a desired carrier signal.. o

For Codan operation no hang-over of the relay |22 is provided such as isprovided for the Vodas operation by the action of the condenser |22connected in parallel with resistance |38 as it is assumed that theradio transmitter from which the intermittent carrier receiver isequipped with suitable circuits to produce a carrier lhang-over similarto that provided by the hang-over feature of the control circuit 300.

operators control circuit 200 The operators control circuit comprisestwo alternative methods of connection, one with the control'unit 240connected as shown in the drawings, for connection to a four-wireextension or telephone subscribers line 233-234, and the other with thecontrol circuit 250 substituted for the circuit 240 for connection to atwo-wire extension or telephone subscribers line 266. These two types ofoperation will be separately described later.

The dial 580 (Fig. 6) really comprises part of I the operators controlunit 200 sothat the operator may select the desired radio frequencychannel in the transmitter by the operation of the dial 600. Theoperation of this dial controls the.

selection mechanism in the 'same manner as the operation of the dial 620previously described.

48-volt direct current from the rectifier 405 of i to the unlteredLitl-volt suppy circuit 202 and is therefore in an operated conditionwhenever the switch 402 is closed to connect the rectifier circuit tothe main power source. In the operated condition of the relay 303 the48volt circuits in the control unit are connected through the relayarmatures to the 48-volt circuits of the transmitter rectifier, theunfiltered sppply 202 being connected throughthe left-hand armature anditsfront contact and the i'lltered supply 20| being connect-ed throughthe right-hand armature and its front contact. In the unoperatedcondition of the relay 203, that is when the transmitter-rectifiercircuit is not operated, the 48- volt circuits of the control unit areconnected to an emergency supplybattery 204 which may be I a battery asindicated, or a portion of a rectied supply for the receiver |00. Thus,whenever the transmitter-rectifier is not connected to the main powersource as may be the case during long periods betweenthe use of theradio equipment,

operating voltage from the battery 304 is available for supervision ofthe extension telephone circuits and for interphone communicationbetween the operators position and any ofthe telephone extensions. i

Radio telephone communication from operators l position 'After thedesired radio frequency channel has been dialed, radio communicationvmay be carried on from vthe operators position and from the extensiontelephone in the following manner: When the operators key 220 is thrownto the up or radio position, the operator may. use his telephone setcomprising the telephone transmitter or microphone 206 and the telephonereceiver 201 for the transmission and reception of radio telephonesignals. The operation of the key 220 arranges the circuit for such useas folows:

1. One side of the operators microphone 206 is connected through the`contact 22| to ground. The other side of the microphone is permanentlyconnected to the low impedance winding of the microphone transformer 205and through the microphone choke coil 208 to the ltered 48-volt supply.

2. Both sides of the high impedance .winding of the microphonetransformer 205 are connected through the key arms1222 and 223 to thetransmitter volume control attenuator 209 which is used to regulate thespeech level supplied to the input circuit of the radio transmitterthrough the leads 2|0 connected lto the primary winding oi thetransformer 208.

3. The operators telephone receiver 201 which is connected to thearmatures 2|3 and 2|4 of the relay 2|2 is connected through the backcontacts of these armatures, resistors 2|5 and 2|B,`1ower arms ofthe key220 to the input sideof Silent coil group 2||-. l

With the circuits arranged as just described, voice frequency currentsin the high impedance winding of the microphone transformer 205 areapplied to the speech input circuit of the transo mitter and will causeoperation lof the voice operated carrier control circuit 300 in thetransmitterreceiver interlock circuit.

When speech is impressed upon the radio transmitter a side tone signalis furnished to the operators telephone receiver 206. The side tone isdeveloped in the radio transmitter volume indicator circuit as describedin a later 'section with the subtitle Monitoring, The volume indicatorcircuit 2| 1 from the output of the monitoring transformer 4|6 isconnected to the radio receiver output circuit throughthe three-wayimpedance matching pads 2|8 and 2|9.

When no speech is impressed upon the radio transmitter an incomingsignal to the radio receiver will reach the operators telephone re-4ceiver through the pads 2|8 and'2l9.`

Four-wire telephmzcextension The operators control unit 200 vpermitsextentype 240. While only one of these umts is shown in' the drawings,it is obvious that additional units with their corresponding keys like24|, may be similarly connected to permit selective connection of theradio system to any of a group of four-Wire extension telephones.

With the extension key 24| thrown to the upper or operator position andthe operators key 220 in the neutral or monitor position, circuitsbetween the subscribers extension and the operators telephone set arecompleted asfollows:

l. The 48-volt circuit through the winding of relay 2 l2 is completed toground through the contact 224 of key 220, contact 242 of key 24|causing the relay 2|2 to operate. In the operated condition relay 2|2completes to ground the 48- volt circuit for the operators microphonethrough its inner right-hand armature, and transfers the operatorstelephone receiver from the radio receiver output circuit to one side ofthe two-way path 230 through its armatures 2l3 and 2 I4. The other sideof the path 230 is connected to the output winding of the microphonetransformer (not shown) is removed from its switch-hook the leads 234are connected together through the extension microphone element and theprimary winding of the extension telephone induction coil. Current fromthe iiltered 48-volt source will then flow from lead 238 through winding236 of relay 235 through the microphone of the subscribers set returningto ground through the winding 231 of relay 235. Speech impressed uponthe subscribers microphone superimposes an alternating current upon thedirect microphone current and speech voltages appear across the windingsof relay 235. 'Ihe subscribers microphone circuit 234 will also beconnected through the upper arms of the key 24|, blocking condensers 26|and 262, through the resistors 23| and 232 and to the output side of thepad 230 and consequently through the front contacts and armatures 2I3and 2|4 of relay 2|2 in the operators receiver 201. The resistors 23|and 232 furnish a connection between the subscribers talking circuit 234and the subscribers listening circuit 233 thus furnishing side tone tothe subscriber.

The circuit just described completes the connection for two-wayinterphone connection between the subscriber and the operator.

The operator permits the subscriber to communicate over the radiocircuit from the fourwire extension telephone connected to the circuits233 and 234 by throwing the extension key 24| to the lower or radioposition. In this position of the key the following circuit arrangementresults:

The 48volt circuit through the winding of relay 2|2 to ground is brokenat the arm 242 of key 24| allowing the operators telephone receiver tobe reconnected to the radio receiver output circuit through the normallyclosed contacts of the operators key 223, that is, with the key 220 inthe neutral position.

The output of the radio receiver after passing through the Silent coilgroup 2|I is connected through the arms 241 and 248 of the key 24| tothe subscribers telephone receiver circuit 233.

'I'he speech circuits from the subscribers telephone transmitter circuit234 are applied through the arm 249 of the key 24| and the blockingcondensers 263 and 264 to the transmitter volume attenuator 209 andthence to the speech input circuit of the radio transmitter.

For supervision of the four-wire telephone extension the key 24| is inits neutral position. When the subscribers telephone set is removed fromthe switch-hook a direct current path is provided between the leads 234,as previously described. Current may then flow from the filteredA1li-volt source to the subscribers microphone circuit and through thewindings of the supervisory relay 235 causing the relay 235 to operate.When the relay 235 operates, the grounded armature provides a path forcurrent from the 1B-volt circuit from ground, armature of relay 235,contacts 245l and 246 of the key 24| in its neutral position,supervisory lamp 265 to the positive 48- volt terminal, causing the lamp265 to light indicating that the subscriber is calling.

When the operator answers the incoming call by throwing the key 24| totheupper position the indicator lamp circuit will be broken for as longas the key is in either upper or lower position and the extension setremains 01T the switchhook. When the extension set is replaced on theswitch-hook after completion of the call, the 48- volt circuit throughthe relay 35 is broken and the relay armature is released fallingagainst its back contact. If the key 24| is then in the lower or radioposition the armature of relay 235 will again supply ground to theindicator lamp indicating to the operator that the radio call has beencompleted.

Two-wire telephone extension For operating the radio system with asubscribers two-wire extension telephone circuit such as the usualcommercial type telephone system, the unit 250 is substituted for theunit 240, the connections being made to the letter terminals asindicated. In this system the conventional commercial type of two-wiresubscribers telephone set (not shown) terminates in the line 266. Withthis circuit the operation of the key 252 permits interphonecommunication between the operator and subscriber and also radio.telephone communication from the remote subscribers stations.

With the operators key 220 in the neutral position the operator mayanswer an incoming cali from the two-wire extension by throwing theextension key 252 to the upper position arranging the circuit forinterphone communication as follows:

1. Ground is connected to the winding of relay 2|2 through the arm 224of switch 220, terminal I-I, upper right-hand arm of key 252 to ground,the operator being furnished a side tone and speech from his microphoneappearing at the terminals D and G in a similar manner as in connectionwith the four-wire circuit.

2. The speech circuit terminating in the terminals D and G is connectedthrough the contacts 253 of key 252 to the arms 261 and 263 of thethree-way impedance matching pads allowing the operators speech currentsto go over the line 266 to the subscribers set.

3. Additional contacts on the key 252 connect the retard coil 269between the same terminals of the resistors 261 and 268 providing a lowresistance path for direct current across the line 266. This directcurrent path is to complete supervisory circuits in commercial orprivate branch Y 9,101,668 exchange telephone oinceJ eduipinent to whichthe by the two-wire extension supervisory relay" 21| line 266maybeconnected. will again operate upon completion of a call.

4. 4Speech` currents originating inthe subscrib- -er's set and comingover theline 266 iilow through is required in the operators controlcircuit as such l side tone circuit is furnished by the circuit o! the`subscribers telephone set itself.

t nected to the radio equipment by closing lthe key In that f -key 252mmaucuon cou-m thus providing a- ClA the neutral position. y

blocking condensers 263 and f264 The two-wire telephone extension may becon- 252 to its lower or radio position. position of the key the'f..extension subscrlbers circuit is completed i'or radio telephonecommunication in the followingLriiar'iner:

I. The two lower left-hand closed contacts` of the key 262 connect theextension line 266 through the resistors21i and 212 oi the three-way pad to the terminals A and'B and thence through the input to the radiotransmitter. v 2. Theoutput oi the radio receiver' after passing throughthe Silent coilgroup 230 terminates in the :terminals J and Kfand-is'their'connected through the two lower right-hand closed contacts oi?the key 262, resistors261 and 266 of the threeway pad to the subscribersextension line 266. Incoming signalstol the radio receiver may thereforego over the two-wire line 266 tothe sub.;

scriber. K

3. The resistors 261 and 266 oi the .three-way pad are also connectedthrough contacts of the direct current path between the conductors oftheextension line 266 for holding Vup supervisory relays in an associatedtelephone exchange equipvolt circuit oi the loperator-'s controlequipment l at the terminal I and to the relay front or holding contact.The armature of the relay 21| is connected to ground through a seriesconnection including one pair of `contacts on each side of the key 252.Thus, when a ringing current is supplied over the line 266, the lrelay21| will be operated and locked up through its holding circuit in the`operated position byb the current from the iS-voit source through theholding winding 213 for as. long a time as the key 252 remains in Thefront contact ofthe relay 21| is also Vconnected to the supervisory lamp215 so that when the relay 21| is operated a circuit from the 48- voltsupply ai; terminal I is provided through the lamp 215.

When the incoming call is answered by closingthe keyV 252 to its upperor iope'rator" position, the ground return circuit from the supervisoryl relay holding winding is opened allowing the relay armature to fallback.l At the same time ground' is also removed from the indicator lamp215 extinguishing` the lamp. I

No provision is made in the control unit wheref vthrough tol the speechHowever. the operator will knowJ when a radio call has been completedby\ monitoring on the .radio circuit. -I

Monitoring 'With the operators key 220 in the neutralA or ."monitpr"position, the operator may listen tor incoming calls in the' output oithe-radio re-y ceiver. In this condition the operators telephonereceiver is also connected' to the volume indicator circuit of the radiotransmittery through the connection 2I1 permitting the'joperator tomonitor speech both to and from' a subscriber.

In the neutral` position .of the operators key 226, the operatorstelephone receiver is connected through closed contacts on the key and tbackncontactson relay `2| 2 Ato the input side o! the Silent-.coil group2| i. ."I'helinput side of this coil group 2|'| connects both' totheaudioirequency output circuito! the radio receiver |00 and to the'radiotransmitter monitoring circuit through the three-way pads 2| 6 and v2|0.l

vIn this manner the operator may hear both sides of the radioconversation when the radio equipment is connected to .a subscriber.When speech froma subscriber is impressed upon the radio transmitterithe Silent coil group 2li being disabled through vthe action of thecontrol relay |22, the subscribers speech in the monitoring circuit isprevented from getting back to the subscriber by the Silent coil group2| i.

With the operators key in the lower position `the operator jis permittedto hear the received signal exactly as it is-heard by the subscriber.

In this position .of the key the operator-fs tele'- phone receiver4 istransferred to the output side of the Silent coil group 2| i enablinghim to detect and. correct am? false operationI of the radio receivercontrol relay |22'.I

Volume indicator The volume lindicator meter 214 may be used to indicatethe speech or tone levelslboth into -the' radio transmitter and out ofthe radio receiver. With the volume indicator key 216 in the lowerposition, as shown inthe drawings, the indicator is connected to theline 2|1 which connects the secondary of the monitoring transformer 4|6of the transmitter, the primary winding of this transformer beingconnected in the plate return circuit of the radio transmitter powerampliner tube as previously described. The nature oi' the circuit issuch that the potential across the volumeindicator meter 216 is a func-ntion of .the speech or tone components oi the power amplifier platecurrent. I With the volume indicator key- 216 in the upper position,lthe volume indicator meter 214 is connected directly across the outputof the radio receiver |00. the operator may adjust the level of thereceived speech always to the same predetermined level most satisfactoryto the subscriber.

The potentiometer 211 is provided for regulat- A ing the sensitivity of.the voice operated radio transmitter controlunit 300 when thesensitivity control switch 36| is in the left-hand position. The purposeof this potentiometer 211 is to select the maximum `permissiblesensitivity ,of the radio transmitter voice operated control unit un-"der varying conditions of room' noise, speakers voice level-and linenoises of any nature.- .v

The transmitter sensitivity potentiometer 211 In that position oi thekey 216 regulates the bias potential applied to the grid of the secondamplifier tube 824 thereby controlling the magnitude of the platecurrent supplied to that tube through the operating winding on thetransmitter carrier control relay 818.

. Radio telegraph communication The system may be used for radiotelegraph transmission by supplying a tone to the radio transmitterspeech input circuit by the operation of the telegraph key 218. Theoscillator 288 which will supply a tone say of approximately 800 cyclesfor transmission of telegraph signals in the following manner:

The tube 28| of the oscillator receives niament heating current andplate supply from the unfiltered 48volt circuit when the tone controlkey 282 is closed. With the oscillator made ready for use by closing thekey 282 the operator may condition the circuit for either M. C. W. or C.W. transmission by closing the key 288 to either the upper or lowerposition, respectively. Thus,

, the key 282 may remain closed to energize the tube 28| during theradio telephone transmission period without interfering with thetransmission of telephone signals provided the key 288 is in the neutralposition.

With key 288 in the upper or M. C. W. position one terminal of theoutput winding 288 of the oscillator transformer is connected throughthe left-hand contact oi the key 288 to the telegraph key 218 and theother side of the winding 284 is connected through the right-handcontact of key 288 to the other side of the input circuit 2I0 to theradio transmitter. At the same time +48-volt battery is applied throughthe righthand contact of key 288, connection 288 through the winding ofthe relay 8I8 of the control unit 308. Relay 8|! is therefore operatedfor as long a time as the key 288 is in the upper or ll. C. W. positionand its upper armature short-circuits the winding of relay 8I8 which ifallowed to operate would hold open the ground circuit to the plate ofthe radio frequency oscillator tube I8 and maintain the oscillator inoperated condition between tone impulses to the speech input circuit.With the transmitter hang-over thus removed, that is, by the snorting ofthe winding of the relay 8M, tone may be supplied to the speech inputcircuit of the transmitter by pressing the telegraph key 218 to causethe carrier control relay 8l8 to operate each time the key is pressedand falling back to the unoperated condition each time the key isreleased. The impressed tone pulses are allowed to pass through theaudio-amplifier comprising' the tubes 808 and 3I0 and thus to modulatethe interrupted carrier wave.

With the key 288 thrown to the lower or C. W. position the circuit isconditioned for the transmission of C. W. telegraph signals. Tone isagain supplied through the telegraph key 218 to the radio transmissionspeech input circuit when the telegraph key is pressed. In thisposition, however, the key 288 connects +48 volts through the connection288 to the ungrounded side of the winding of the relay 8|! causing it tobecome operated in which condition it performs vtwo functions, namely:(1) the input to the second audio-frequency ampliiler tube 8I8 isshorted through the upper armature of the relay 8|2 preventing theimpressed tone pulses from being ampliiled and applied to the carrier ofthe radio transmitter; (2) the outer lower armature of the relay 8I2short-circuits the winding of hangover relay 8I8 removing the carrierhang-over between tone impulses applied to the speechinputcircuitasinthecaseforltaw. transmission.

What is claimed is:

1. A two-way radio communication system comprising a radio transmitter.a radio receiver. an electric discharge device having an input circuitconnected to the signal input to the radio transmitter, a iirst relayhaving a winding connected in the space current path of said device andoperated by the increased space current due to signal waves in theinput, means responsive to the operation of said relay for enabling thetransmitter for the generation and transmission of a carrier wave, asecond relay responsive to the operation of the first relay forestablishing an auxiliary circuit for enabling the radio transmitter.time controlled means for maintaining said second relay operated for aperiod after the release of said nrst relay suihciently long to preventundesired interruption of the carrier between syllables or words spokenin rapid succession, a third relay operated simultaneously with thefirst relay for disabling the radio receiver, and a fourth relayoperated by the nrst relay for providing an auxiliary operating circuitfor said third relay, and time controlled means for maintaining saidfourth relay Operated for an interval of the order of 8 to 10milliseconds after the release of the second relay.

`il. In a two-way radio communication system, a radio transmitter, aradio receiver. means for normally maintaining said transmitter in aninoperative condition and said receiver in an operative condition. anelectric discharge device having an input circuit connected to thesignal input circuit of said transmitter, a source of space current forsaid device, a plurality of relays having windings connected in serieswith said source in the space current path oi said device and operatedon the increased space current of said device due to signal waves insaid input circui means responsivev to the operation of one of saidrelays for rendering said transmitter operative, means responsive to theoperation of another of said relays for rendering said receiverinoperative, a first and a second hang-over relay, means responsive tothe operation of said one relay for operating said hang-over relays,means responsive to the operation of said ilrst hang-over relayforestablishing an auxiliary circuit arrangement for maintaining saidtransmitter in an operative condition irrespective of the condition ofsaid one relay, means responsive to the operation of said secondhang-over relay for establishing' a circuit for maintaining said otherrelay operated irrespective of the condition of the space current pathof said device, time controlled means for maintaining said rst hang-overrelay operated for a period after the release of said one relaysufficiently long to prevent undesired interruption of the transmissionby said transmitter between syllables or words spoken in rapidsuccession, time controlled means for maintaining said second hang-overrelay operated for a few milliseconds after the release of said ilrsthang-over relay, and means responsive to waves received by said receiverfor opening the space current circuit of said device.

3. In a two-way radio communication system,

a radio transmitterl a radio receiver, means for normally maintaining'said transmitter in an inoperative condition and said receiver in anoperative condition, an electric discharge device havcircuit o! saidradio transmitter, a sourcel of spacel current for said device, aplurality o! relays connected in series with said source in the spacecurrent path o! said device and operated on the increased space currentot said device due to the signal waves in said input circuit, meansresponsive -to the operation of one of said relays for rendering saidtransmitter operative, means responsive to the operation of yanother ofsaid relays for rendering said receiver inoperative, a

1 hang-over relay connected to be operated by the operation of said onerelay. means responsive to the operation of said other relay forestablishing an auxiliary circuit arrangement for maintaining `saidtransmitter in an operative condition irrespective of the condition ofsaid one relay, and

time controlled means for maintaining said hang-over relay operated fora period aiterthe release of said one relay suillciently long topreoperative condition and said receiver in an operative` condition, anelectric discharge device having an input circuit connected to thesignal input circuit of said transmitten'a source of space current forsaid device, a radio transmitter controlling relay, 'a group of radioreceiver controlling relays, connections for including the windings ofsaid transmitter controlling relay and said receiver controlling relaysin series with said source in the space current path of said device sothat all of said relays are operated on the increased space current ofsaid device due to the signal waves in said' input circuit, meansresponsive to the operation of said radio transmitter controlling relayfor rendering said transmitter operative, means responsive to theoperation of said radio receiver controlling relays for rendering boththe radio frequencycircuit and the audiofrequency circuit of saidradioreceiver inoperative, a rst and a second hang-over relay, meansresponsive t0 the operation of said transmitter controlling relay foroperating said hang-over relays, means responsive to the operation oi'said first hang-over relay for establishing auxiliary circuitarrangements for maintaining said transvmittel' in an operativecondition irrespective of the condition of said transmitter 'controllingyrelay, means responsive to the operation of said second hang-over relayfor establishing a circuit for maintaining said radio receivercontrolling relay operated irrespective of thecondition of the spacecurrent path of said device, time controlled means for maintainingsaidrst hangover relay operated for a period after the release of saidone relay suii'iciently long to prevent undesired interruption of theoperative condition of ing an input circuit connected to the signalinput t3 the space current circuit of said discharge device.-

5. Inl a/.two-way radio transmission system a.4

radio receiver, a radio transmitter employing electric Adischargedevices, a source of power for energizing said devices, means responsiveto the signal wave input of said transmitter tor controlling anoperative condition of said transmitter to render said transmitteroperative for transmission of radio waves in the presence oi a signalwave input and to prevent the transmission of radio waves in the absenceoi a signal wave input, time controlled means operative a predeterminedtime after the initiation of its operation to interrupt the. supply ofpower from said source to said discharge devices, and means responsiveto the cessation of signal input for initiating the operation of saidtime controlled means.

6. In a two-way radio transmission system, a radio receiver, a radiotransmitter employing electric discharge devices, a source of cathodeheating current and a source of space current for said devices, meansresponsive to the signal input to said transmitter for controlling anoperative condition of said transmitter to render said transmitteroperative yfor the transmission of 4 radio waves in the presence of asignal wave input and to prevent the transmission of radio waves in theabsence of a signal wave input, time controlled `means operative apredetermined time after the initiation o! its operation to interruptthe 'supply ot space lcurrent from said source Vto said dischargedevice, means responsive to the cessation of the signal wave input forinitiating the operation of said time controlled means,y and a secondtime controlled means operative a predetermined time after theinitiation of its operation to interrupt the supply of cathode heatingcurrent to said discharge devices, and means responsive to the ilnaloperation of the first time controlled means for initiating theoperation of said second time controlled means.

7. In` a two-way radio communication system, a radio receiver, a radiotransmitter of the vacuum tube type, a power supply for said radiotransmitter," a control circuit comprising a vacuum tube, a relay forcontrolling an operative condition of said radio transmitter, a secondrelay for controlling an operative condition of said radio receiver, anda series circuit including the windings of said relays and theanode-cathode circuit of said vacuum tube, means responsive to thesignals to be transmitted for rendering said vacuum tube conductivewhereby said relays operate to enable said transmitter and disable saidreceiver, time controlled meansoperative la predetermined time after theinitiation of its operation to interrupt the supplyof power to saidradio transmitter, `and means responsive to the operation of said rstrelay for initiating the operation of said time controlled means.

8. In a two-way radio transmission system, according to claim 7, asecond time controlled vmeans operative a predetermined time aftertheinitiation of its operation to interrupt the supply of cathode heatingcurrent to the vacuum tubes of said radio transmitter, and meansresponsive to the naloperation of the first-mentioned time controlledmeans for initiating the operation oi' said second time controlledmeans.

9. In a two-way radio communication system,l

a radio receiver, a radio transmitter, a plurality of sets oi' tuningunits for said transmitter, each set being adapted for tuning saidtransmitter for transmitting at a different frequency, a selec- I torswitch control mechanism -for selectively connecting said sets of tuningunits in circuit in said transmitter, means operated by said selectorswitch control mechanism for connecting high voltage'power to saidtransmitter, relay means operative in a normal condition forrenderingsaid transmitter inoperative and in an operative position forrendering said transmitter operative for the transmission oi radiowaves, time controlled means operative a predetermined time after theinitiation oi its operation to release said selector switch controlmechanism whereby the high voltage power supply and the sets of tuningunits are disconnected from said transmitter, and means operated by theoperation oi said. selector switch control mechanism or by the normalcondition oi said relay means for initiating the operation -of said timecontrolled l0. In a two-way radio communication system, a radioreceiver, a radio transmitter, a plurality oi sets of tuning units iorsaid transmitter, each set being adapted ror tuning said transmitter iortransmitting at a dierent frequency, a selector switch control mechanismfor selectively connecting said sets oi? tuning umts in circuit in saidtransmitter, means operated by said selector switch control mechanismfor connecting high voltage power to said transmitter, means tornormally maintaining said transmitter in an inoperative condition andsaid receiver in an operative condition, an electron dischargedevicehaving an input circuit connected to the signal input circuit of saidtransmitter, a source of space current ior said device, a plurality ofrelays having windings connected in series with said source and thespace current. path of said device and operated on the increased spacecurrent of said device due to signal waves in said input circuit, meansresponsive to the operation of one of said relays/for rendering saidtransmitter operative, means responsive to the operation ot another o!said relays ior rendering said receiver inoperative, a ilrst and a.second hang-over relay, means responsive to the operation oi said onerelay for operating said hang-over relay, means responsive to theoperation of said nrst hang-over relay for establishing an auxiliarycircuit arrangement for maintaining said transmitter in an operativecondition irrespective of the condition of said one relay, meansresponsive to the operation of said second hang-over relay forestablishing a circuit for maintaining said other relay operatedirrespective oi the condition of the space current path of said device,time controlled means for maintaining said rst hang-over relay operatedfor a period after the release of said one relay suiilciently long toprevent undesired interruptions oi the transmission oi said transmitterbetween syllables or words spoken in rapid succession. time controlledmeans for maintaining said second hang-over relay operated for a i'ewmilliseconds after the release of said ilrst hang-over relay,

means responsive to waves received by said receiver for opening thespace current circuit oi said device, time controlled means operative apredetermined time after the initiation ot its operation to release saidselector switch control mechanism whereby the high voltage power supplyand the sets of tuning units are disconnected from said transmitter, andmeans operated by the meansior normally maintaining said transmitterinoperative for initiating the operation of the last-mentioned timecontrolled means.

1l. In a two-way radio communication system, a radio receiver, a radiotransmitter employing a plurality of vacuum tubes. a plurality of setsof tuning units for said transmitter, each set being adapted for tuningsaid transmitter for transmitting at a different frequency. a source forsupplying space current to said vacuum tubes.

a selector switch control mechanism for selectively connecting said setsoi tuning units in circuit in said transmitter, means operated by saidselector switch control mechanism ior completing the circuit from vsaidsource for supplying space current to said vacuum tubes. a controlvacuumtube having an input circuit connected to the signal input circuit ofsaid trans mitter, means for deriving space current from. said sourceior said control vacuum tube including the means operated by saidselector switch control mechanism for completing the circuit from saidsource to the vacuum tubes oi. said transmitter, a plurality' of relayshaving windings connected in series with said source in the spacecurrent path oi' said control vacuum tube and operated on the increaseinspace current oi said control vacuum tube due to the signal waves insaid input circuit, a control circuit including contacts of one oi.'said relays, an inductance 'coil and a resistor for grounding the anodeoi' one oi the vacuum tubes oi said radio trans,

mitter to render said transmitter inoperative when said one relay is ina normal condition, means responsive to the operation oi another oilsaid relays for rendering said receiver inoperative, a ilrst and asecond hang-over relay, said ilrst hang-over relay having contacts inseriesin said circuit for grounding the anode of one of the vacuum tubesot said transmitter when said ilrst hang-over relay is in a normalposition, means responsive to the operation 'of said one relay foroperating said hang-over relays whereby when said ilrst hang-over relayis operated said circuit for grounding the anode oi one of the vacuumtubes oi said transmitterls open to render said transmitter operative,means responsive to the operation oi said second hangover relay forestablishing a circuit for maintaining said other relay operatedirrespective of the condition of the space current path of said controlvacuum tube, time controlled means for maintaining sa'id ilrst hang-overrelay operated for a period after the release oi' said one relaysumciently long to prevent Vundesired interruption oi the operativecondition of said transmitter between syllables or words spoken in rapidsuccession, time controlled means i'or maintaining said second hang-overrelay operated for a few milliseconds after the release of said rsthang-over relay, means responsive to the waves received by saidreceiverfor opening the space current circuit of said control vacuum tube, relaymeans having a winding connected in said control circuit for groundingthe anode oi one of the vacuum tubes oi said transmitter and arranged tobe operated a predetermined time after its initial energization, meansresponsive to the operation of said last-mentioned relay means torelease said selector switch control mechanism whereby the power supplycircuit for the space current of the vacuum tubes of said radiotransmitter is interruptedand the set of tuning units is disconnectedfrom the transmitter.

l2. In a radio transmitter employing an elecl plying space current tosaid device, means ior

